Computers are often used with monitors or displays. These monitors typically provide good black and white or color images if the area where the display is located is not too bright. However, if the ambient light directed at the display is too bright, then glare, or light reflected from the screen, can make it tiresome to look at the information displayed on the screen. In severe lighting environments, such as outdoors and/or in direct sunlight, it can be nearly impossible to see what is displayed on the screen. Furthermore, the low back-lighting of these displays often makes it difficult to read them when viewing the display screen at an angle.
One type of computer monitor, which is attractive for its compactness and light weight, is a back-lit liquid crystal display (LCD). A light source, usually located behind the display's liquid crystal panel, emits light which must pass through the panel out towards the user. There is usually a diffuser located between the light source and the LC panel to provide uniform back lighting so that the user can not see the light source behind the LC panel.
If more light was emitted by the display screen, the signal (information displayed on the screen) to noise (glare) ratio could be significantly improved. This would, in turn, make it easier, and possible in even the brightest locations, to view what is displayed. The increased light would also allow viewing of the screen from a wider angle relative to a position directly in front of the screen. However, to increase the light emitted by the LC panel would require a much brighter back lighting source.
The use of a brighter light source presents several problems. A first problem is that increasing the amount of light transmitted through the screen also significantly increases the amount of thermal energy absorbed by the LC panel. This prolonged, excessive thermal exposure can cause the LC panel to fail.
A second problem with significantly increasing the amount of emitted light is that the risk of the light source overheating also increases. To avoid such overheating, a large amount of heat must be dissipated to the outside of the monitor or display cabinet. Conventional heat transfer devices are simply not equipped to handle such a high volume of thermal energy in such a compact environment.
U.S. Pat. No. 3,330,130 to Schraith, et al. teaches a cooling device for a fluorescent lamp. However, the system is clearly too bulky for an LC display, and lacks the heat transfer characteristics necessary to dissipate enough heat to cool a light source bright enough to provide the desired back lighting.
A third problem with increasing the power of the light source is that as the temperature surrounding the source increases beyond a certain point, the efficiency of the light source (i.e. the light emitted relative to the power consumed) decreases. Furthermore, the elevated temperatures reduce the life span of the light source, such that the mean time between failure is higher with higher temperatures.
An additional problem with LC displays is the possibility of damage to the light source. The preferred light source for these displays is typically a glass flourescent tube, which is highly susceptible to breakage. Considering the harsh conditions faced by portable computers, it is desirable to protect the light source from shock and vibration which may damage it.